1. Field of the Invention
The present invention generally relates to an endless steel band for a belt press and the use of the endless steel band for the production of chipboard.
2. Description of the Prior Art
Double-belt plants for producing strands of any length from cold hardened or duroplastic materials are known from examples in EP 0 732 183 A. In these double-belt plants, steel bands with a thickness of from 2.8 mm to 3.5 mm are used. Such bands must have high flexibility, as they are applied on drums with a diameter, for example, between 1.5 m and 3 m. After the bands are applied, they are be driven in the belt press. In order to form certain structures, such as raised wood grains, on the surface of a 1.2 mm thick melamine resin plate, it is known to first form corresponding structures, such as depressions, on the surface of the steel bands. Then the steel band presses the resin plate and the raised wood grains can be obtained on the final product. Such depressions on the steel bands are obtained by etchings, especially with ferric chloride solution. The formats of the structures are usually fixed photographically or digitally. The starting material for making the steel band with surface structures is usually a steel band with a polished surface, which has a roughness of RZ 50 μm. Generally, the depressions are usually shallow on the surface of the steel band, because there is the fear that the steel band with deep depressions on its surface may not resist the tension strains. Usually, steel bands are held under pressure by the drums situated at both ends of the band. In addition, the band may prematurely break when it is applied to the belt press.
Chipboards normally have substantially plain and smooth surfaces, which are required for further uses, such as, gluing with decoration plates and similar materials. The smooth surface that is not skid resistant is also known in plastic plates used, for example, in the sanitary field. However, under certain circumstances, chipboards must be skid resistant. For example, chipboards may be walked on or used in a wet environment. Chipboards may also be inclined at an angle of 60° relative to a horizontal surface. The skid resistance can be determined by testing the angle relative to a horizontal surface at which the skidding takes place.
Different processes are known in order to obtain such antiskid chipboards. Initially, an additional sheet is provided between a band and the plastic material to be pressed during the pressing process. Although a steel sheet is used, its life is, e.g. 4,000 to 8,000 hours, which is relatively short.
In a later development, the plastic material that is already substantially hardened is pressed with embossing rollers to form depressions on the chipboards. Depressions on the chipboard have several disadvantages. If the surface is polluted, the adhesion with other materials is difficult. In addition, depressions cause damages in the structure and the stability of the chipboard is reduced. Sometimes, the chips and the wood glue tend to swell, as there is no more seal on the chipboard surface.